There are several ionizing methods for the conventional LC-MS. Each ionizing method has its features and has difficulty in ionizing some substances.
A LC as a separating apparatus enables the measurement of a large variety of substances including low-polarizing substances and high-polarizing substances.
Various systems have been developed to deal with a variety of samples by a single ionizing method.
Those systems are described in Yoshiaki Karo et al., "Hitachi LC-MS analyzer M-1000", HITACHI SCIENTIFIC INSTRUMENT NEWS, Vol. 34, No. 1, (1991).
Each of those ionizing methods has certain features and is capable of ionizing only a specific group of samples and is incapable of ionizing all kinds of samples.
On the other hand, the LC-MS is desired to be able to analyze a variety of substances for LC.
Therefore, a MS provided with two ion sources has been proposed. A known art uses an API method and an ion source in combination to enhance ionizing efficiency.
This known art uses a main ion source of the API method and an auxiliary ion source of an electron impact type connected in series to the main ion source and ionizes neutral molecules which could not be ionized by the API by electron impact to increase the quantity of ions so that the sensitivity of mass spectrometer is substantially enhanced. Techniques relating to this known art is disclosed in Japanese Patent No. 1078632.
A LC-MS provided with an atmospheric ionization ion source and a chemical ionization ion source which are used selectively to analyze a variety of substances has been proposed. Techniques relating to this LC-MS are disclosed in Japanese Patent Laid-open (Kokai) No. 4-109160.
Although the aforesaid known MS is provided with two ion sources, there are restrictions on the operating condition of the sample supply system, and only a limited number of combinations of two ion sources are possible. Therefore, the MS is able to analyze limited substances and is unable to utilize the advantageous capability of separating a variety of substances of a LC, even if the MS is connected directly to the LC.
No attempt was made to use the MS in combination with an ESI method that exhibits an excellent function in ionizing ionic, high-polarizing compounds and hence the MS is incapable of analyzing polymeric compounds.
The present invention has been made to solve those problems in the related art and it is therefore an object of the present invention to provide an atmospheric ionization MS provided with a plurality of ion sources to be selectively used, connected directly to a LC capable of analyzing a variety of substances to utilize the advantages of the LC, and capable of measuring a variety of objects.